Hydraulic Drives for Bridges Considering the New DIN Standard ...

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partial safety factors y, and combination values ly for ultimate limit stare analys~s (except for farigue strength proof) of steel structures - - Basic combinattorts I Exceptional 1 I con~btnations ' I Hydrodynam~c ad~ons Water road I I -135 The most substantial changes as against previous issues of the standard are: a) The calculation of the steel structure and -as far as possible - also of the machinery construction is based on the concept of limit state design using partial safety factors and combination factors. b) Steel structures and machinery constructions are generally not regarded as being constructions under static load. Therefore, fatigue strength proofs are required. C) The (computat~onal) service life of steel struaures, machinery elements and electrical equipment is given. Considering their function, hydraulic steel structures must be designed simple, robust and operationally safe. For steel structures a service life of 70 years has to be assumed, for machine elements, including their electrical equipment for 35 years.This does not refer to wear parts. Apart from some fundamental determinations, the standards DIN 19704 and 19705, issue 1976, contained only a few regulations regarding the design of oil hydraulic drives. The new revision of DIN 19704-1, -2 and -3, issue 1997, which replace the old standards 19704 and 19705, therefore took into account the new developments in the field of oil hydraulics, so that this standard now reflects state of the an. d) For the first time, manufacturing tolerances are given for the steel In the previously valid standards DIN 19704, issue 1976, the following load structures of firmly installed pans and hydrogates. The objective of this cases were relevant for the calculation and rating of the drives: is to ensure that the calculation assumptions, e.g. bearing conditions, comply with the design to a sufficient degree. In addition, the aspects of Normal operational case "NB" se~iceability have been taken into account for the manufacturing Specific operational case "BB" tolerances. Exceptional load case "AL" e) In view of their importance hydraulic drives are dealt with in detail. The Investigations have shown that for approximately 80 % of all supplied technical progress In the field of hydraulic drives has been significantly systems, the specific operational case "88" are relevant for the calculation promoted by Mannesmann REXROTH. It was therefore possible to and design of the drives. For this reason the new standard norm DIN 19704. consider the basic principles for design and matters of operational 1 provides only the operational case "moving" for the drives. safety, reliability and fatigue strength in a comprehensive form in the new regulations.
If "Exceptional actions" have to be additionally taken into account (e. g. If the operating pressures are considerably lower than 250 bar, double-sided drive of a closing-off structure - failure of drive), the drive components with lower continuous operating pressures/nominal pressures must be automatically shut down when these actions occur. At that can also be selected. This is also permitted with~n a hydraul~c system, e. g. moment, only a single traversing to one of the two end positions for auxiliary drives. "closing-off structure open" or "closing-off structure closed" w~ll be permitted or, if required, moving into a repair position. For this purpose Be actions of drives such as the stalling torque of the motor, rhe braking the client must make unmistakable determinations which comprise both torque or the setting values of pressure reJief valves (which have to be operational measures. secured by sealing) in oil hydraulic systemsQre cons~dered as controlled, variable actions. Their values have to be included in the calculation as In the previously valid standard DIN 19704 the following maximum characteristic values of the highest possible transmiss~on of forces. The operating pressures were determined: reactive effects of the highest possible transmission of forces have to be traced in all essential machine pans, for which an ultimate state analysis Normal operational case "NB" = 220 bar (except for the fatigue strewngth proof) is required, up to the connection Specific operational case "BB" = 250 bar to the steel structure of the gate or, if required, up to their bearlng points. Exceptional load case "AL" = 300 bar These reactiv effects creates some problems which using mechanical hoists It must be noted that these determinations have proven useful over the were an acurate overload protection is difficult to achive. With hydraulic last 20 years since the DIN 19704 - issue 1976 was published. For this hoists this problem can be solved easily by installing maximum pressure reason, in the new DIN the orders of the maximum operating pressures relief valves directly on the cylinder. Specially when the power pack is far were in principle maintained. away from the cyl~nder the maximum pressure relief valve on the pump has to be set to a higher pressure to obtain the pressure drop in the pipes. The new standard DIN 19704 - 1 now provides only one operational case In case the gate is blocked this higher pressure can not occur in the "moving", with the permissible maximum operating pressure being 250 cylinder by adjusting the cylinder to exactly the pressure required for the bar. If "exceptional actions" have to be taken into account, during the maximum load. presence of which operating movements do not occur, the permissible static pressure in the cylinder or hydraulic motor must not exceed 300 bar. (The pressures mentioned here are the set values of the pressure relief valves, see chapter "Determination of computational operating pressures"). In view of the rating of drives, this results in a striking difference between the "old" and the "new" DIN. In the exceptional load case it was acceptable (at least not explicirly excluded in the "old" DIN), to run an emergency mode at a maximum pressure of 300 bar over a longer period of time when these conditions occured. According to the new DIN 19704 this is no longer permitted. As already mentioned, the permissible maximum pressure during "moving" amounts to 280 bar which is justified as follows: All the components of renowned manufacturers are approved for an operating pressure of 280 to 31 5 bar. The actuators such as solenoids, return springs, etc. are rated for these pressures. Thus, sufficient safety is provided at maximum operating pressure in order to ensure operational safety also under unfavourable conditions, e. g. low temperatures. From this consideration results the requirement in DIN 19704 - 1 that for all hydraulic components, the continous operaring pressure/ nominal pressure must be 25 % higher than the computational operating pressure. Example of an arrangement of the pressure control valves in conjunction with a wngle acting, single rod cylinder
Page 1 and 2: Heavy Movable Structures, Inc. SEVE
Page 3 and 4: Herausgeber Mannesmann Rexroth AG D
Page 5: - constructions for rlver control a
Page 9 and 10: The figure below shows a system wit
Page 11 and 12: If the cylinder is mounted by means
Page 13: The hydraulic pipe system has to be

Hydraulic Drives for Bridges Considering the New DIN Standard ...

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